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Subject[PATCH 2/6] blk-cgroup: pass blkg_rwstat structures by reference
Date
Returning a structure generates rather bad code, so switch to passing
by reference. Also don't require the structure to be zeroed and add
to the 0-initialized counters, but actually set the counters to the
calculated value.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
block/bfq-cgroup.c | 15 +++++++++------
block/blk-cgroup.c | 31 ++++++++++++++++---------------
include/linux/blk-cgroup.h | 14 +++++++-------
3 files changed, 32 insertions(+), 28 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index b3796a40a61a..66abc82179f3 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -935,9 +935,9 @@ static u64 bfqg_prfill_stat_recursive(struct seq_file *sf,
static u64 bfqg_prfill_rwstat_recursive(struct seq_file *sf,
struct blkg_policy_data *pd, int off)
{
- struct blkg_rwstat sum = blkg_rwstat_recursive_sum(pd_to_blkg(pd),
- &blkcg_policy_bfq,
- off);
+ struct blkg_rwstat sum;
+
+ blkg_rwstat_recursive_sum(pd_to_blkg(pd), &blkcg_policy_bfq, off, &sum);
return __blkg_prfill_rwstat(sf, pd, &sum);
}

@@ -975,9 +975,12 @@ static int bfqg_print_stat_sectors(struct seq_file *sf, void *v)
static u64 bfqg_prfill_sectors_recursive(struct seq_file *sf,
struct blkg_policy_data *pd, int off)
{
- struct blkg_rwstat tmp = blkg_rwstat_recursive_sum(pd->blkg, NULL,
- offsetof(struct blkcg_gq, stat_bytes));
- u64 sum = atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
+ struct blkg_rwstat tmp;
+ u64 sum;
+
+ blkg_rwstat_recursive_sum(pd->blkg, NULL,
+ offsetof(struct blkcg_gq, stat_bytes), &tmp);
+ sum = atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_WRITE]);

return __blkg_prfill_u64(sf, pd, sum >> 9);
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 6f79ace02be4..7d6bf9b03e24 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -602,8 +602,9 @@ EXPORT_SYMBOL_GPL(blkg_prfill_stat);
u64 blkg_prfill_rwstat(struct seq_file *sf, struct blkg_policy_data *pd,
int off)
{
- struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd + off);
+ struct blkg_rwstat rwstat = { };

+ blkg_rwstat_read((void *)pd + off, &rwstat);
return __blkg_prfill_rwstat(sf, pd, &rwstat);
}
EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
@@ -611,8 +612,9 @@ EXPORT_SYMBOL_GPL(blkg_prfill_rwstat);
static u64 blkg_prfill_rwstat_field(struct seq_file *sf,
struct blkg_policy_data *pd, int off)
{
- struct blkg_rwstat rwstat = blkg_rwstat_read((void *)pd->blkg + off);
+ struct blkg_rwstat rwstat = { };

+ blkg_rwstat_read((void *)pd->blkg + off, &rwstat);
return __blkg_prfill_rwstat(sf, pd, &rwstat);
}

@@ -654,8 +656,9 @@ static u64 blkg_prfill_rwstat_field_recursive(struct seq_file *sf,
struct blkg_policy_data *pd,
int off)
{
- struct blkg_rwstat rwstat = blkg_rwstat_recursive_sum(pd->blkg,
- NULL, off);
+ struct blkg_rwstat rwstat;
+
+ blkg_rwstat_recursive_sum(pd->blkg, NULL, off, &rwstat);
return __blkg_prfill_rwstat(sf, pd, &rwstat);
}

@@ -736,6 +739,7 @@ EXPORT_SYMBOL_GPL(blkg_stat_recursive_sum);
* @blkg: blkg of interest
* @pol: blkcg_policy which contains the blkg_rwstat
* @off: offset to the blkg_rwstat in blkg_policy_data or @blkg
+ * @sum: blkg_rwstat structure containing the results
*
* Collect the blkg_rwstat specified by @blkg, @pol and @off and all its
* online descendants and their aux counts. The caller must be holding the
@@ -744,12 +748,11 @@ EXPORT_SYMBOL_GPL(blkg_stat_recursive_sum);
* If @pol is NULL, blkg_rwstat is at @off bytes into @blkg; otherwise, it
* is at @off bytes into @blkg's blkg_policy_data of the policy.
*/
-struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
- struct blkcg_policy *pol, int off)
+void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
+ int off, struct blkg_rwstat *sum)
{
struct blkcg_gq *pos_blkg;
struct cgroup_subsys_state *pos_css;
- struct blkg_rwstat sum = { };
unsigned int i;

lockdep_assert_held(&blkg->q->queue_lock);
@@ -767,12 +770,10 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
rwstat = (void *)pos_blkg + off;

for (i = 0; i < BLKG_RWSTAT_NR; i++)
- atomic64_add(blkg_rwstat_read_counter(rwstat, i),
- &sum.aux_cnt[i]);
+ atomic64_set(&sum->aux_cnt[i],
+ blkg_rwstat_read_counter(rwstat, i));
}
rcu_read_unlock();
-
- return sum;
}
EXPORT_SYMBOL_GPL(blkg_rwstat_recursive_sum);

@@ -958,14 +959,14 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)

spin_lock_irq(&blkg->q->queue_lock);

- rwstat = blkg_rwstat_recursive_sum(blkg, NULL,
- offsetof(struct blkcg_gq, stat_bytes));
+ blkg_rwstat_recursive_sum(blkg, NULL,
+ offsetof(struct blkcg_gq, stat_bytes), &rwstat);
rbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_READ]);
wbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_WRITE]);
dbytes = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_DISCARD]);

- rwstat = blkg_rwstat_recursive_sum(blkg, NULL,
- offsetof(struct blkcg_gq, stat_ios));
+ blkg_rwstat_recursive_sum(blkg, NULL,
+ offsetof(struct blkcg_gq, stat_ios), &rwstat);
rios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_READ]);
wios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_WRITE]);
dios = atomic64_read(&rwstat.aux_cnt[BLKG_RWSTAT_DISCARD]);
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 06236f56a840..3ee858111274 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -224,8 +224,8 @@ int blkg_print_stat_ios_recursive(struct seq_file *sf, void *v);

u64 blkg_stat_recursive_sum(struct blkcg_gq *blkg,
struct blkcg_policy *pol, int off);
-struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
- struct blkcg_policy *pol, int off);
+void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
+ int off, struct blkg_rwstat *sum);

struct blkg_conf_ctx {
struct gendisk *disk;
@@ -700,15 +700,14 @@ static inline void blkg_rwstat_add(struct blkg_rwstat *rwstat,
*
* Read the current snapshot of @rwstat and return it in the aux counts.
*/
-static inline struct blkg_rwstat blkg_rwstat_read(struct blkg_rwstat *rwstat)
+static inline void blkg_rwstat_read(struct blkg_rwstat *rwstat,
+ struct blkg_rwstat *result)
{
- struct blkg_rwstat result;
int i;

for (i = 0; i < BLKG_RWSTAT_NR; i++)
- atomic64_set(&result.aux_cnt[i],
+ atomic64_set(&result->aux_cnt[i],
percpu_counter_sum_positive(&rwstat->cpu_cnt[i]));
- return result;
}

/**
@@ -721,8 +720,9 @@ static inline struct blkg_rwstat blkg_rwstat_read(struct blkg_rwstat *rwstat)
*/
static inline uint64_t blkg_rwstat_total(struct blkg_rwstat *rwstat)
{
- struct blkg_rwstat tmp = blkg_rwstat_read(rwstat);
+ struct blkg_rwstat tmp = { };

+ blkg_rwstat_read(rwstat, &tmp);
return atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_READ]) +
atomic64_read(&tmp.aux_cnt[BLKG_RWSTAT_WRITE]);
}
--
2.20.1
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